Actions: Automatic and Semi-automatic actions

So far, we've studied a number of different actions and weapons that allow users to fire multiple times without stopping to reload. Now we will discuss the actions of modern weapons, mainly semi-automatic and automatic actions.

In the actions we've studied earlier, such as bolt-action, lever action, pump action etc., the user has to fire the weapon and then manipulate some lever manually, in order to eject the old spent cartridge and load in a new cartridge. In many cases, these weapons have multiple cartridges loaded into the magazine and manipulating the lever strips a new cartridge from the magazine.

In the case of revolvers, the act of pulling back the hammer or the trigger rotates the cylinder and brings upon a new round to be fired.

In the early 1850s, it was realized that if the loading operation could be automated, then this would lead to more rapidly firing firearms. This lead to several innovations in firearms technology. We will study some of the principal actions in the next few posts, such as the Gatling action, chain action, blowback action, gas operated action, recoil action etc.

This might be a good stage to gloss over the differences in various actions:

• Gatling: This consists of a multiple barrel weapon. The various barrels rotate about a central axis and fire one at a time. The barrels may be rotated by hand or by an electric motor.
• Chain driven: This is a single barrel weapon that uses a electric motor and a drive chain to drive the mechanisms to load a cartridge, fire it and eject the spent cartridge.
• Blowback: In this type of mechanism, some of the expanding gases from a fired cartridge push back on the cartridge. The bolt holding the cartridge in place is not locked and is only held by spring pressure. The spent cartridge case is pushed back against the bolt and these are together forced back against the spring pressure and this force helps eject the old cartridge, cock the weapon and load a new cartridge into place. The barrel of a blowback weapon is generally fixed and does not move when the weapon is fired.
• Gas operated: In this type of action, as the gas escapes through the front of the barrel, some of it is bled off and fed back to actuate the ejection of the spent cartridge and load a new one.
• Recoil operated: In this type, the bolt and barrel are locked at the point that the cartridge is fired (a key difference from the blowback action where the bolt is never locked.) After the cartridge is fired, the barrel and bolt move together in the opposite direction from the bullet, due to Newton's third law of motion. The barrel stops moving at one point and the bolt unlocks and continues to move backward to cock the weapon, eject the old cartridge and load a new cartridge.

Blowback actions are generally used many smaller pistols and recoil operated weapons on some bigger pistols and shotguns. Gas operated mechanisms are generally used for assault rifles and some pistols. Gatling and chain actions are now generally used for larger fully automatic weapons, most of which are too heavy to be carried by a single individual and fall somewhat out of the range of what can be called "firearms".